1. Field of the Invention
This invention relates to a novel surfactant water flooding enhanced oil recovery process. The invention also relates to an alkylphenyl ether propane sulfonate composition of matter. The invention further relates to solutions containing an alkylphenyl ether propane sulfonate. The solutions are useful for recovering petroleum in an enhanced oil recovery process.
2. Prior Art
The crude oil which has accumulated in subterranean reservoirs is recovered or produced through one or more wells drilled into the reservoir. In the initial production, the crude oil is produced by primary recovery techniques wherein only the natural forces present in the reservoir are utilized to produce the oil. However, upon depletion of these natural forces and the termination of primary recovery a large portion of the crude oil remains trapped within the reservoir. Additionally, many reservoirs lack sufficient natural forces to be produced by primary methods from the very beginning. Recognition of these facts has led to the development and use of many enhanced oil recovery techniques. Most of these techniques involve injection of at least one fluid into the reservoir to produce an additional amount of crude oil therefrom. Some of the more common methods are water flooding, steam flooding, CO.sub.2 flooding, polymer flooding, surfactant flooding, caustic flooding, and in situ combustion.
Water flooding, which involves injection of water into the subterranean oil reservoir for the purpose of displacing the crude oil from the pore spaces of the reservoir rock toward the producing wells, is the most economical and widely used of the enhanced oil recovery methods. Nevertheless, water does not displace oil with high efficiency because of the immiscibility of water and oil and because of the high interfacial tension between them.
Surfactant flooding involves the addition of one or more surface active agents or surfactants to the water flood for the purpose of minimizing the water flooding problems mentioned above. This has been an area of active interest in the art of enhanced oil recovery methods for many years. U.S. Pat. No. 3,302,713 discloses the use of petroleum sulfonates as effective surfactants in oil recovery operations. Other surfactants proposed for use in oil recovery processes include alkyl sulfates, alkyl aryl sulfates, ethoxylated alkyl or alkyl aryl sulfates, alkyl sulfonates, alkyl aryl sulfonates, and quaternary ammonium salts.
One major drawback of most of the above surfactants is the fact that they will precipitate where the water hardness, i.e. the concentration of divalent ions including calcium and magnesium, is relatively high. Since many formations contain very hard water, these surfactants are useless in some applications.
Another problem which frequently detracts from the performance of surfactants is that many degrade chemically and/or in performance at high formation temperatures. Petroleum sulfonates as well as other alkyl or alkylaryl sulfonates are relatively stable at room temperatures and at temperatures encountered in some subterranean petroleum reservoirs. However, these materials are usually not effective in the presence of high salinities and/or high formation water hardness. Conversely, nonionic surfactants such as polyethoxylated alkyl phenols are effective for surfactant flooding in formations containing high salinity water or hard water but these materials become insoluble at temperatures in the range of from about 100.degree. F. to about 125.degree. F. Therefore, if a reservoir is at this temperature, these materials are not effective.
One type of anionic surfactant which is frequently effective for use as a co-surfactant in combination with petroleum sulfonates or alkyl ro alkylaryl sulfonates is a water soluble sulfate salt of a polyethoxylated alcohol or alkyl phenol. However, the sulfate linkage is highly sensitive to temperature and hydrolysis or other permanent degradation of the sulfate linkage may take place at high temperatures. For example, the sulfate salt of a polyethoxylated alkyl phenol having an alkyl chain link of about nine carbon atoms and having approximately four or five ethylene oxide groups per molecule is degraded at about 140.degree. F. This is not an unusually high temperature for certain reservoirs and since the surfactant will ordinarily be present in the formation for long periods of time, even years, the thermal stability of the surfactant solution becomes extremely important.
It is an object of this invention to provide surfactants which are tolerant of formation water salinity hardness and which are tolerant of temperatures in excess of 120.degree. F. for long periods of time without hydrolyzing or becoming insoluble.